A terrible virus has wiped out much of the human population and Scotland is now a wasteland, overrun by wild dogs. Toby's little sister Sylvie is dangerously ill and his family set out in a boat along the Aberdeenshire coast in desperate search of medicine. On their journey they battle for food and fuel, try to outwit lawless pirates and struggle to stay one step ahead of the ever-more powerful dogs and their mighty leader Cerberus. But will they find a cure for Sylvie before it's too late?